One important character of the third generation mobile communication system is the imbalance of the traffics of uplink and downlink, and the traffic of the downlink will be generally more than that of the uplink. Aiming at this demand, 3GPP (3rd Generation Partnership Project) introduces HSDPA (High Speed Downlink Packet Access) characteristic in the 3G Specification.
In the HSDPA characteristic, a higher speed downlink packet service is provided to improve the utilization efficiency of frequency spectrum by introducing AMC (Adaptive Modulation and Coding) and HARQ (Hybrid Automatic Retransmission Request) technologies and relevant technologies for reducing the processing time delay at the network.
The AMC technology determines the capacity of the present channel according to the circumstances of the channels (channel state information CSI) and determines a proper coding and modulation mode according to the capacity so as to send information at its maximum and realize a higher speed; and for the quality changes of the channel, the AMC can provide a corresponding changed modulation and coding solution, thereby improving the transmission speed and the utilization efficiency of the frequency spectrum.
The HARQ is an error correcting method which combines the traditional ARQ (Automatic Retransmission Request) technology and the FEC (Forward Error Correct) technology. The code sent by a sender can not only detect errors, but also have certain error correcting ability. When a receiver receives information, it will correct errors automatically if the error is within the error correcting capability, and if the errors are beyond the error correcting capacity of an error correcting code but can be detected, the receiver will feedback a corresponding signal to the sender for requesting a retransmission.
In the HSDPA technology, a HS-DSCH (High Speed Downlink Shared Channel) and a MAC-hs (Media Access Control-high speed) sub-layer are newly introduced. At the network side, the MAC-hs is realized in the Node B for the data transmission of the HS-DSCH transmission channel. In the Node B, each cell has a MAC-hs entity, and the MAC-hs not only accomplishes HS-DSCH data processing and dispatching, but also is in charge of the management and configuration of HSDPA physical resources. The MAC-hs comprises functional entities such as the entities for flow control, dispatching/priority control, HARQ function, and TFRC (Transport Format and Resource Choice). In the MAC-hs entities at the Node B side, each UE corresponds to a HARQ entity, which adopts a N-Channel SAW (See And Wait) Protocol, i.e., the HARQ entity adopts the N-channel-SAW-HARQ protocol. One HARQ entity corresponds to multiple HARQ processes, and in the present protocols of 3GPP regarding TD-SCDMA, the HARQ entity of one UE can comprise at most 8 HARQ processes, and different HARQs are marked by process IDs. One HS-DSCH TTI corresponds to a HARQ process. At the UE side, a UE corresponds to a MAC-hs entity, comprising functional entities of the HARQ function, distribution function, re-arrangement function and decomposition function. Wherein the HARQ entity and the HARQ entity in the Node B entity are peer entities, they comprise the same number of HARQ processes, each process forms one-to-one corresponding protocol entities through the process Ed and the process at the Node B side, for receiving the MAC-hs PDU (Protocol Data Unit) data packet, lithe receiver receives data correctly, it will feedback a ACK signal through a following described uplink HS-SICH channel (High Speed Shared Information Channel), and the HARQ process at the Node B side releases the data packet. On the other hand, if the receiver does not receive the data correctly, then it caches the soft data and feedbacks a NAK signal through the HS-SIGH, and the process at the sender side retransmits the data packet, i.e., the HARQ entity processes the retransmission of the MAC-hs PDU data packet according to the process.
In the HSDPA technology of the TD-SCDMA system, the newly introduced HS-DSCH transmission channel is mapped to a newly introduced HS-PDSCH (High Speed Physical Downlink Shared Channel). The HS-PDSCH channel is shared by multiple users in a cell in the mode of time division or code division. The TTI (Transmission Time Interval) of the HS-PDSCH is 5 ms. The HS-PDSCH carries the service data of a user, and the relevant control information for receiving HS-PDSCH is transmitted through a newly introduced accompanying HS-SCCH (High Speed Shared Control Channel), and the HS-SICH is used for transmitting the uplink feedback information. Therefore, these three physical channels are composed of a physical layer closed loop, they conduct processing and transmission in the TTI unit of 5 ms, and these shorter TTI can self-adapt to the time-varying characteristic. Wherein, the control information carried on the HS-SCCH channel comprises: HARQ Process ID, redundant edition, new data identification, HS-SCCH cycle serial number HCSN, UE ID, MF (Modulation Form), identification of transmission block size and physical channel resources; the feedback information carried on the HS-SICH channel comprises: recommended modulation form RMF, recommended transmission block size RTBS and the confirmation information ACK/NAK for confirming whether the data are transmitted correctly. Besides, for transmitting a RRC signaling, the 3GPP further defines the accompanying physical channels of the uplink and downlink in the R5, for carrying the RRC signaling relevant to HSDPA.
According to the present 3GPP protocol, in the TD-SCDMA system, the cell corresponds to the carrier frequency by one-to-one. The configuration method of HSDPA-related channel resources in a single-carrier cell is as follows: one HS-DSCH, multiple HS-SCCHs, a HS-SICH corresponded to each HS-SCCH by one-to-one. When the network side configures HS-DSCH resources for a UE, one to four HS-SCCHs are configured, thus constituting a HS-SCCH set. and meanwhile, a HS-SICH corresponded to each HS-SCCH by one-to-one is configured. In the process of sending HS-DSCH data, for each HS-DSCH TTI, the Node B sends a HS-DSCH-related control channel on a HS-SCCH channel, the UE obtains the information through reading the channel, and sends feedback information on a HS-SICH channel which corresponds to the HS-SCCH by one-to-one. At the Node B side, each HS-DSCH TTI, for a certain UE, chooses a HS-SCCH for the UE by the MAC-hs, i.e., sending the HS-DSCH-related control channel to the UE on the HS-SCCH channel. At the UE side if the HS-SCCH set does not have a HS-SCCH which can be allocated to the UE for using, then the UE monitors the HS-SCCH set continuously, by the comparison between the “UE Identification” information read from the HS-SCCH and the identification of the UE itself, the HS-SCCH actually allocated to the UE is found until the HS-SCCH channel allocated to the UE is found, and from the next TTI, the HS-SCCH is only monitored and received, the control information carried by the HS-SCCH is used to receive HS-DSCH data, and feedback information is sent at a HS-SICH channel corresponding to the HS-SCCH, until at a certain TTI, the UE can not read a UE identification being consistent with itself in the HS-SCCH, or can not read the HS-SCCH, then the UE re-monitors the allocated HS-SCCH set until a HS-SCCH allocated to the UE is found.
The above description is the HSPDA technology in the present 3GPP protocol relevant to TD-SCDMA system. However, the TD-SCDMA system of the present 3GPP protocol is a single-carrier system, i.e., one cell corresponds to a carrier frequency, and the width of the frequency spectrum of a single-carrier frequency is 1.6 M, as the TD-SCDMA adopts a comparative narrow-band TDD mode, the theoretical peak value speed at the single carrier can reach 2.8 Mbps, and the down-peak-rate that can be provided by the single-carrier is lower, and can not meet satisfactorily the demand of the operator on future high speed packet data service. Therefore, technical improvements should be made on the basis of the single-carrier cell HSDPA technology to meet the higher requirement of the operator for high speed packet data service.